When producing a flexible printed wiring board or a rigid wiring board, a liquid resist or, a dry film formed from a resin composition on a copper clad laminate as a base, and a polyimide film provided with an adhesive are commonly used as a cover material. Furthermore, a photosensitive resin composition (liquid photosensitive resist) and a photosensitive dry film which are photosensitive are also used as a photosensitive cover film. Examples of the constituent materials of these include polybenzimidazole resins, polybenzoxazole resins, and polyimide resins which have excellent heat resistance. However, in terms of ease of resin production and production cost, polyimide resins especially are very useful.
However, flexible printed wiring boards and rigid wiring boards have a laminate structure of organic and inorganic materials. Depending on the materials constituting the laminate, warping of the substrate can occur. Warping can be expressed by the following formula based on the physical properties of the respective constituent materials. Therefore, while there are several approaches, considering the case of a polyimide type cover material, these wiring boards can be prevented from warping by reducing the elastic modulus of the film itself which is made of the polyimide resin. To cope with such a demand, it has been proposed to use a siloxane diamine as one of the plurality of diamine components constituting the polyimide resin (Patent Document 1). Furthermore, it is also required to improve the film-forming properties and chemical resistance of the polyimide resin which uses such a siloxane diamine. To meet these demands, a vinyl ether residue is introduced into the polyimide resin as a reaction group which reacts with an acrylate serving as a crosslinking agent to form a crosslinking point.
      (    Warping    )    =            ∫              T        cure                    T        0              ⁢                            E          f                          1          -                      v            f                              ⁢              (                              α            f                    -                      α            s                          )            ⁢                          ⁢              ⅆ        T                Tcure: Temperature applied on the laminate    Ef: Elastic modulus of material    αf: Coefficient of thermal expansion of material    αs: Coefficient of thermal expansion of substrate    νf: Constant    [Patent Document 1] Japanese Patent Application Laid-Open. No. 2003-131371